Focus magnet assembly for cathode ray tubes



June 4, 1968 AKIO OHKOSHI ET AL 3,387,158

FOCUS MAGNET ASSEMBLY FOR CATHODE RAY TUBES Filed March 31, 1966 2 Sheets-Sheet 1 CUQLIO Uhkoshi Senm' 772i ao/Qa.

yoshiharu Kal'agin June 4, 1968 AKIO OHKOSHI ET AL 3,387,158

FOCUS MAGNET ASSEMBLY FOR CATHODEYFAY TUBES Filed March 31, 1966 2 Sheets-Sheet 2 Inzen'l'mrs.

akio Ohkoshi Senri 77113401. goshiharu Kgragiri 1:3 fir"; H7135.

United States Patent 3,387,158 FOCUS MAGNET ASSEMBLY FOR CATHODE RAY TUBES Akio Ohkoshi, Senri Miyaoka, and Yoshiharu Katagiri, Tokyo, Japan, assignors to Sony Corporation, Tokyo, Japan, a corporation of Japan Filed Mar. 31, 1966, Ser. No. 539,072 Claims priority, appiication Japan, Apr. 14, 1965, 40/ 29,930 6 Claims. (Cl. 313-84) ABSTRACT OF THE DISCLOSURE The invention is directed to a focusing magnet assembly for a cathode ray tube and includes a plurality of magnets mounted about the electron beam path of the tube so as to substantially reduce the axial intensity of the fringing flux fields of the focus magnets. The focus magnet assembly includes a support sleeve of the generally hollow cylindrical shape for mounting about the neck of the cathode raytube and including a plurality of outstanding stopper members. A clamp ring is fixed about the sleeve for securing the sleeve to the neck of the cathode ray tube.

A-n annular shielding ring is mounted about the sleeve at one end thereof to protect the deflection coils of the cathode ray tube from the magnetic flux of the focus magnet assembly.

N The present invention relates to television receivers and is particularly directed to a new and improved focus magnet assembly for the cathode ray tube or kinescope of a television receiver.

The focus magnet assembly of the present invention is of particular utility when employed in conjunction with a post-deflection acceleration cathode ray tube of the general type such as that depicted and described in US. patent application, Ser. No. 357,164 of Satoshi Shimada, entitled, Cathode Ray Tube, which was filled on Apr. 3, 1964, and is assigned to the same assignee of the present application, and is now abandoned.

In this particular type of cathode ray picture tube, the electron beam which is density modulated with video information at the electron gun is accelerated and deflected in a relatively low energy and low velocity state between the electron gun and a mesh screen juxtaposed but spaced from the phosphor 1ight-producing screen. The potentials between the phosphor screen and the mesh screen are such as to accelerate the electron beam to a suflicient extent so as to properly excite the phosphor of the screen to reproduce the transmitted image. The advantage of such a cathode ray tube is that low power is needed to defleet the electron beam. The electron beam of such a tube may be deflected at a greater angle, with greater ease than is conventional for other types of tubes. This advantage is particularly useful in a portable television receiver.

Some problems are encountered, however, with a postdeflection electron beam acceleration tube. These are de focusing of the picture and distortion caused by geometry of the tube and the nature of the low energy beam. The intrabeam effect of repulsion between the like charge of the individual electrons has a greater effect because of the relatively longer period of travel of the beam and tends to defocus the beam.

It is a general object of the present invention to provide a new and improved magnetic focusing assembly for use with a color television receiver for use with a cathode ray tube.

Another object of this invention is to provide such an improved focus magnet assembly having reduced leakage flux.

It is a further object of this invention to provide such a magnetic focus magnet assembly which is especially useful when used in a post-deflection acceleration-type cathode ray tube.

Other objects, features and advantages of the present invention will be readily apparent from the following detailed description of certain preferred embodiments thereof taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a sectional side view of a conventional hollow cylindrical or annular shaped focus magnet depicted in a generally schematic manner;

FIG. 2 is a graphical depiction of the intensity of the axial component of the focus magneic field along the annular axis of the focus magnet depicted in FIG. 1;

FIG. 3 is a generally schematic diagram similar to that of FIG. 1 illustrating the principles of the present invention;

FIG. 4 is a graphical representation similar to that of FIG. 2 of the axial magnetic field intensity of the magnet assembly of FIG. 3;

FIG. 5 is a sectional view, largely in schematic representation, of a television receiver including a cathode ray tube employing a magnetic focus assembly in accordance with the present invention; and,

FIG. 6 is a detailed side plan view, with parts broken away, to show interior parts of a particular magnetic focus assembly constructed in accordance with the principles of the present invention mounted on a television kine scope.

Referring to FIG. 1 there is depicted a conventional focusing magnet 7 of a hollow cylindrical or annular shape. The focusing magnet 7 may be of a permanent magnetic material or comprise a coil, as shown, wound in a generally annular shape through which a direct current is passed. The magnet 7 is, in use, commonly positioned about the neck portion of the cathode ray tube for focusing an electron beam on the screen. A short discussion of such a focusing magnetic coil may be found in Basic Television Principles and Servicing by Grob, McGraw- Hill Television Series, New York, 1954, Second Edition pp. 4041.

The magnet 7 is of generally rectangular cross-section with two planar surfaces 7a and 7b which face in opposite direct'ions normal to the magnets central annular axis Z and are separated *by the thickness of the magnet. The magnet 7 is normally magnetized parallel to its annular axis Z so that one of the surfaces 7a or 7b represents one polarity. For example, the surface 7a may consist of entirely the north magnetic pole, the surface 7b consisting entirely of the south magnetic pole. Under this arrangement, an electron traveling along the axis Z will sense a permanent magnetic field H in the Z axis direction.

As depicted in FIG. 2, the intensity in the positive Z direction of the magnetic field H is shown by the curve 9. The leakage flux field portions are represented by the curve positions 9a and 9b. The effect of the leakage flux field-s 9a and 9b is a reduction of resolution of the electron beam passing through the focus magnet.

In use, the magnet 7 would normally be mounted about the neck of a cathode ray tube between the conventional electron gun and the deflection coils so that the normal path of the electron beam from the cathode ray tube electron gun would be along the axis Z.

Referr ng now to FIG. 3, there is depicted the arrangement of the magnets or coils in accordance with the principles of the present invention. It has been discovered that the de-grading of the resolution of the electron beam focusing may be decreased by using the basic arrangement of FIG. 3. As there depicted, .a pair of hollow cylindrical or annular magnets 11a and 11b, is positioned about the common annular axis Z adjacent to one another and separated by a gap g. Each of the magnets 11a and 11b has a generally rectangular cross-section with planar surfaces 11a and 11b, similar to the surfaces 7a and 7b in shape. The surfaces 11a and 11b face outwardly, whereas surfaces 11a' and 11b face one another across the gap g. In accordance with the present invention, the magnet coils are operated so as to produce polarities at surfaces 11a and 11b of the same type. Thus, the surfaces 11a and 11b may be in the north pole as indicated by the letter N, While the surfaces 11a and 11b may be in the south pole. In this configuration, the flux intensity pattern H along the Z axis, as depicted in FIG. 4, is produced. The S-shaped curve 22 has a low value intensity 22a and 22b resulting from the leakage flux of the two magnets. Curve 23a represents the magnetic field intensity contribution of the magnet 11a While the curve 23b represents the magnetic field intensity contribution of the curve of the magnet 11b. Both curves 23a and 23b, except for the inversion of the polarity of the intensity caused by the reversal of the poles of the magnet 11a, are substantially identical with that of the curve 9 of FIG. 2.

The focal length of a magnetostat-ic lens, such as the lens created by the magnet 7 or the magnets 11a or 11b, may be expressed by the equation:

where f is the focal length and H is the axial component of the magnetic field. It will be observed that as the focal length is related to the square of the intensity of the field H the focus magnet of FIGS. 3 and 4 acts without regard to the polarity of H Thus, either north or south magnetic poles may face one another without changing the focusing effect.

Referring now to FIG. there is depicted a television receiver 10 including a cathode ray tube or kinescope 12 of the general type described in the above-mentioned application for United States Letters Patent. About the neck portion of the kinescope 12 is mounted a focus magnet assembly 11 constructed in accordance with the principles of the present invention. The cathode ray tube 12 includes a glass face panel 12a and a generally cylindrical neck portion 120 which are inter-connected by a generally conical-shaped portion 12b which extends from one end of the cylindrical portion 120 to the periphery of the face panel 12a, where there is deposited and formed a phosphor surface 13 of the type described in more detail in the above-mentioned patent application. The surface 13 includes a conductive metallic coating which is connected to a high voltage source which may be, as depicted, an 8 kilovolt positive potential source. Adjacent to but spaced from the phosphor screen 13, within the tube 12, is a screen mesh 14. The mesh 14 may be connected, as depicted, to a source of high voltage =les-s than that of the screen 13 such as a 4 kilovolt positive voltage source. The interior surface of the conical portion 12b of the picture tube 12 is preferably coated with a conductive metallic covering 16 to form an accelerating electrode for the electron beam, which electrode 16 may be connected to a high voltage source such as the 4 kilovolt source connected to the grid 14. Mounted about the neck 120 of the tube 12, adjacent and juxtaposed to the conical portion 12b of the tube 12, is a conventional deflection yoke 15. The yoke serves to deflect the electron beam which is produced by an electron gun generally indicated by the numeral 21. The electron gun 21 comprises a cathode 17, a control grid 18, a screen grid 19 and an anode 20'. The anode 20 may be conveniently connected to the interior coating 16. The detected light intensity information of the television receiver is conventionally applied between the control grid 18 and the cathode 17 so as to intensity modulate the electron beam with this information. The electron beam from the gun 21 is then deflected across, or caused to scan at an extremely rapid rate the screen 13. The scanning is caused by the signals applied to the deflection yoke 15 which deflects an electron beam from the normal path along an axis Z' toward the various portions of the mesh screen 14 and phosphor screen 13. The electron beam is preferably accelerated in a low energy level by the anode 20, the electrode 16 and the mesh screen 14. Thus, the electron beam may be deflected by relatively low energy fields generated by the coils 15. This results in a considerable saving in the power consumption of a receiver employing this type of tube.

The proper energy level or velocity for the modulated electron beam to excite the phosphors of the screen 13 is obtained by the acceleration caused 'by the potential difference between the voltage on the mesh screen 14 and the phosphor screen 13. For example, a 4 kilovolt difference across the short distance between the mesh screen 14 and the phosphor screen 13 accelerates the electrons from the screen 14 to achieve high energy impact upon the phosphor screen 13 to thereby produce light from the phosphor screen 13 at the point of impact.

Referring now to FIG. 6 there is depicted one particular example of a magnetic focus assembly constructed in accordance with the principles of the invention explained above. The assembly 30 is mounted about the neck 31 of cathode ray tube 32 of the type described in the above-mentioned United States application for Letters Patent. The assembly 30 is mounted between the signal input neck and 312, out of which project the conventional connector pins 33, and conventional deflection yoke 34. The pins 33 are connected to the various electrodes of the electron gun mounted within the neck 31. The neck 31 has a transverse diameter D of a more reduced size than is conventional. The assembly 30 comprises a supporting sleeve 35 which is preferably of a polyester resin material and has a plurality of longitudinally extending narrow slits 36a and 36b formed therein at circumferentially spaced areas of its forward and rearward facing circular ends 35a and 35b. The slits 36a and 36b each extend inward from the ends 35a and 35b for only a minor portion of the longitudinal extent of the sleeve 35. The sleeve 35 is formed with an interior diameter of approximately the exterior diameter D of the neck 31 to achieve a snug fit thereon. The sleeve 35 may be further secured to the neck by a clamp ring 37 mounted about the sleeve 35 in the area of slit 36b. The ring 37 may include a tightening screw 37a. The clamp ring 37 serves to further decrease the effective diameter of the sleeve 35 in the area of the slits 36b and to thereby more securely affix the sleeve 35 and assembly 30 to the neck 31 of the tube 32. The sleeve 35 has a longitudinally extending segment 350 of decreased outside diameter, co-extensive with the forward slits 36a for receiving a generally annular-shaped shielding ring 38. The ring 38 may have an inside diameter such as to crimp the slitted portion near the end 35a to achieve a more secure mounting of the assembly 30 upon the forward portion of the neck 31. The ring 38 is maintained in its forward position on the sleeve 35 by means of a plurality of circumferentially spaced outstanding tabs or stoppers 350. formed as a unitary structure with the sleeve 35 at its forward end 35a.

The shield ring 38 functions to protect the deflection yoke from leakage flux. The ring 38 has an annular cutout portion or bore 38a formed at its interior or rearwardly facing surface for loosely receiving an outstanding flange portion of a generally annular-shaped centering magnet 39. The centering magnet 39 is formed with an outstanding flange portion for entering the cavity 38a formed in the magnet 39. The magnet 39 is frictionally engaged and because of its relatively loose fitting within the cavity 38a of the shield ring 38, may be positioned about a continuous range of positions about the neck 39 so as to properly center the electron beam. Adjacent to and in frictional engagement against the centering magnet 39 there is provided a first generally hollow cylindrical or annular-shaped magnet 11a, the in terior diameter of which approximately equals the exterior diameter of the sleeve 35 for mounting therewith. The magnet 11a is adjacent to a similar magnet 11b which may be also characterized as hollow cylindrical or annular in shape. Both magnets 11a and 11b are of ferrite magnetic material. The magnet 11a is adjacent to but spaced from the magnet 11b by a gap-defining projection 35g of the polyyester resin sleeve 35 therebetween. Each of the ferrite magnets 11a and 11b is polarized parallel to its annular axis and arranged so as to have substantially reduced intensity of the fringing flux fields along their common axis. As depicted, the magnet 11b is magnetized with its north pole facing rearward and the magnet 11a is magnetized with the north pole facing forward so that the poles face each other across the gap g. Also further provided is a ring 40 for moving the focus magnet assembly. The ring 40 is spaced between the magnets lla and 11b and extends therebetween. The dimension D is somewhat less than twice the dimension L and the gap g is approximately one-third of the dimension L.

The magnets 11a and 11b have a similar longitudinal extent L. In the specific embodiment of FIG. 6, the length D is equal to 13.2 mm., while the dimension L is equal to 7.5 mm. The gap g is approximately 2.5 mm. In employing a conventional focusing magnet such as the magnet 7 of FIG. 1 in a similar environment as FIG. 6, the magnet would be approximately mm. in longitudinal dimension. Thus, the magnet assembly of the present invention is approximately the same size as the previous magnet assemblies. The width of the magnet shown in FIGS. 5 and 6 is smaller than that of the magnet shown in FIG. 1 and is approximately one-half of the magnet shown in FIG. 1.

It will now be apparent that there has been described a new and improved focusing magnet assembly which has special provisions for the application of a low velocity electron beam post-deflection acceleration cathode ray tube of the type described. It should be apparent that many modifications may be made in the device Without departing from the spirit of the invention, e.g., the polarity of each magnet 11a and 11b of the figures described may be reversed so that the south magnetic poles shall face one another without affecting the focusing of the assembly. Furthermore, three or more magnets may be employed using the general principle of the super-position of their axial magnetic field intensity pattern so as to achieve the object of applicants invention. Similarly the arrangement of the invention may be positioned elsewhere along the electron beam path to achieve the same end. However, the above-described structure is the presently preferred structure and teaches the presently best known mode of operation of the invention.

It will be understood that various modifications may be suggested by the embodiment disclosed, but we desire to claim within the scope of the patent warranted hereon all such modifications as come within the scope of the claims.

We claim as our invention:

1. A focus magnet assembly for mounting about the neck portion of a kinescope adjacent the deflection coils, comprising:

a polyester resin supporting sleeve of a generally hollow cylindrical shape for mounting about the neck. of the kinescope, said sleeve having first and second circular end edges and a plurality of longitudinal slits formed at each of the end edges, extending only a minor portion of the length of said sleeve, and circumferentially spaced thereabout, said sleeve further including a plurality of outstanding stopper members at said first end and an outstanding gap-defining projection for-med therefrom between said first and second ends,

a clamp ring afiixed about said sleeve near said second end for decreasing the effective diameter of said sleeve and thereby securing said sleeve to the neck portion of the kinescope;

an annular shield ring mounted about the sleeve adjacent to the outstanding stopper members of said sleeve and functioning to protect the deflection coil from magnetic leakage flux;

an annular centering magnet mounted adjacent to said shield ring about said sleeve, and

a pair of generally annular ferrite magnets mounted about said sleeve juxtaposed on opposite sides of the gap-defining projection of said sleeve, said ferrite magnets being magnetized parallel to their annular axis and arranged with similar magnetic poles being juxtaposed to said gap-defining projection so that their fringing magnetic flux fields substantially cancel one another.

2. The focus magnet assembly as claimed in claim 1 in which said magnets are of the electromagnetic type and are of a generally annular configuration.

3. The focus magnet assembly as claimed in claim 1 in which said magnets are of the permanent magnetic type and are of a generally annular shape with the axis of magnetization parallel to the annular axis and are arranged with their annular axes along the electron beam path.

4. The focus magnet assembly as claimed in claim 3 in which said plurality of magnets are two and are arranged with like poles facing one another across a selectively small gap.

5. The focus magnet assembly as claimed in claim 4 in which said annular shaped ferrite magnets are of a similar configuration with a generally rectangular crosssection with an interior annular diameter dimension of approximately twice their longitudinal dimensions and a gap dimension of approximately one-third of their longitudinal dimension.

6. The focus magnet assembly as claimed in claim 5 in which the interior annular diameter dimension is approximately 13.2 mm., the longitudinal dimension of each of the ferrite magnets is 7.5 mm. and the gap dimension is approximately 2.5 mm.

References Cited UNITED STATES PATENTS 2,202,620 5/1940 Boersch 31384 2,849,636 8/1958 Verhoef et a1. 3l384 2,873,413 2/1959 Reynst 335212 JAMES W. LAWRENCE, Primary Examiner.

V. LAFRANCHI, Assistant Examiner. 

